Pagers and portable telephones are made with built-in notification devices, which have vibrators as well as buzzers, as a means of call notification in conferences and other locations where it is inappropriate to use an audible alarm. If the vibration mode is switched on in advance, the vibrator is driven instead of an alarm being sounded when a call comes in, and the recipient is made aware of the call by means of the vibration.
In the past, this vibration has been created by a small motor, an eccentric weight attached to the shaft of the motor such that a vibration it generated when the battery-driven motor is caused to rotate.
As portable electronic equipment including pagers and portable telephones has become smaller and lighter, further miniaturization of motors has become necessary, but there are limits to the miniaturization of call notification devices with both vibrators and buzzers. Moreover, because the amount of vibration from battery drive is fixed, there is a further drawback in that there are individual differences in the strength of vibration necessary.
To resolve this problem, the applicants have developed a speaker-type electromagnetic actuator that does not use the small motor of U.S. Pat. No. 5,528,697.
This electromagnetic actuator is an epochal product that combines the function of selecting the vibration ring, buzzer ring or tone ring as a vibration mode into the same unit as the speaker function. It is so constituted that when a given frequency is impressed on a coil, the interaction of the magnetic field of the magnets and the current impressed on the coil generates vibration in a vibration plate in the case of a low frequency or a resonant tone in a diaphragm in the case of a high frequency. Moreover, because it is possible to control the amount of vibration and the frequency, the amount of vibration can be adjusted and set at the level desired by the individual.
As portable telephone equipment has become widely used, there has been demand for an electromagnetic actuator that can suppress the external leakage of magnetic flux and also have good frequency characteristics even though small in size. There has also been demand for high durability within the usage environment of portable electronic equipment with internal electromagnetic actuators, such that they do not break even if the user drops them. There is further demand, from the perspective of cost reduction, for reduction of the number of parts and for ease of assembly.